Shielding for high-voltage semiconductor-on-insulator devices

ABSTRACT

Integrated circuits having doped bands in a substrate and beneath high-voltage semiconductor-on-insulator (SOI) devices are provided. In one embodiment, the invention provides an integrated circuit comprising: a semiconductor-on-insulator (SOI) wafer including: a substrate; a buried oxide (BOX) layer atop the substrate; and a semiconductor layer atop the BOX layer; a plurality of high voltage (HV) devices connected in series within the semiconductor layer; a doped band within the substrate and below a first of the plurality of HV devices; and a contact extending from the semiconductor layer and through the BOX layer to the doped band.

BACKGROUND

One useful aspect of semiconductor-on-insulator (SOI) structures is thatthey permit the use of high-voltage SOI devices, such as diodes, fieldeffect transistors (FETs), thyristors, and bipolar transistors. Stillhigher voltages may be achieved by connecting a plurality of suchdevices in series. However, doing so increases the difference in voltagepotential between the device and an underlying substrate. Thisdifference increases in each downstream device in the series. As such,the type and number of high-voltage SOI devices that may be connected inseries is ultimately limited by the difference in voltage potentialbetween the terminal device and its underlying substrate. Too great adifference in voltage potential will result in degradation of thebreakdown voltage (V_(br)) of the series device, making the device“leaky.” This can adversely impact the efficiency of the series device,sometimes to a degree that the series device fails. For example, in thecase of five high-voltage (i.e., 30 V) diodes connected in series, thevoltage at the terminal diode would theoretically be 150 V. However, ator near the terminal diode, this may result in too great a difference involtage potential with the substrate, resulting in the voltage at theterminal diode being less than 150 V.

FIG. 1 shows an integrated circuit 100 including a substrate 10, aburied oxide (BOX) layer 20, and a semiconductor layer 30. Withinsemiconductor layer 30 are a plurality of HV SOI devices, here shown asdiodes 40A-40D, connected in series. Diode 40A comprises a p-dopedportion 42A and n-doped portion 44A. For the sake of clarity, thep-doped portions and n-doped portions of diodes 40B-D are not labeled,but are similar to p-doped portion 42A and n-doped portion 44A of diode40A.

As can be seen in FIG. 1, a difference in voltage potential 41A betweendiode 40A and substrate 10 is less than a difference in voltagepotential 41B between diode 40B and substrate 10. A difference involtage potential 41C between diode 40C and substrate 10 is greater thandifference in voltage potential 41B, and a difference in voltagepotential 41D between diode 40D (the terminal diode) and substrate 10 isgreater still. As noted above, difference in voltage potential 41D maybe so great that the breakdown voltage degrades, resulting in voltageleakage.

SUMMARY

Integrated circuits having doped bands in a substrate and beneathhigh-voltage semiconductor-on-insulator (SOI) devices are provided.

A first aspect of the invention provides an integrated circuitcomprising: a semiconductor-on-insulator (SOI) wafer including: asubstrate; a buried oxide (BOX) layer atop the substrate; and asemiconductor layer atop the BOX layer; a plurality of high voltage (HV)devices connected in series within the semiconductor layer; a doped bandwithin the substrate and below a first of the plurality of HV devices;and a contact extending from the semiconductor layer and through the BOXlayer to the doped band.

A second aspect of the invention provides an integrated circuitcomprising: a semiconductor-on-insulator (SOI) wafer including: asubstrate; a buried oxide (BOX) layer atop the substrate; and asemiconductor layer atop the BOX layer; at least one high voltage (HV)device within the semiconductor layer; an n-doped band within thesubstrate and below the at least one HV device; and a contact extendingfrom the semiconductor layer and through the BOX layer to the n-dopedband.

A third aspect of the invention provides an integrated circuitcomprising: a semiconductor-on-insulator (SOI) wafer including: a p-typesubstrate; a buried oxide (BOX) layer atop the substrate; and asemiconductor layer atop the BOX layer; a first high voltage (HV) deviceand a second HV device connected in series within the semiconductorlayer; a first n-doped band within the substrate and below the first HVdevice; a second n-doped band within the substrate and below the secondHV device; a first contact extending from the semiconductor layer andthrough the BOX layer to the first n-doped band; and a second contactextending from the semiconductor layer and through the BOX layer to thesecond n-doped band, wherein the first n-doped band and the secondn-doped band are separated within the p-type substrate by a space, aportion of the first n-doped band extends laterally beyond an end of thefirst HV device, and a portion of the second n-doped band extendslaterally beyond an end of the second HV device.

A fourth aspect of the invention provides a semiconductor-on-insulator(SOI) wafer including: a substrate; a buried oxide (BOX) layer atop thesubstrate; a semiconductor layer atop the BOX layer; a first doped bandwithin the substrate; a second doped band within the substrate; a firstcontact extending from the semiconductor layer and through the BOX layerto the first doped band; and a second contact extending from thesemiconductor layer and through the BOX layer to the second doped band.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

These and other features of this invention will be more readilyunderstood from the following detailed description of the variousaspects of the invention taken in conjunction with the accompanyingdrawings that depict various embodiments of the invention, in which:

FIG. 1 shows a schematic cross-sectional view of an integrated circuithaving a plurality of semiconductor-on-insulator (SOI) devices connectedin series.

FIG. 2 shows a schematic cross-sectional view of an integrated circuitaccording to an embodiment of the invention.

FIG. 3 shows a schematic cross-sectional view of an integrated circuitaccording to an other embodiment of the invention.

FIG. 4 shows a schematic cross-sectional view of an integrated circuitaccording to yet another embodiment of the invention.

FIG. 5 shows a partial schematic cross-sectional view of an integratedcircuit according to still another embodiment of the invention.

FIG. 6 shows a schematic cross-sectional view of an integrated circuitaccording to yet another embodiment of the invention.

It is noted that the drawings of the invention are not to scale. Thedrawings are intended to depict only typical aspects of the invention,and therefore should not be considered as limiting the scope of theinvention. In the drawings, like numbering represents like elementsbetween the drawings.

DETAILED DESCRIPTION

FIG. 2 shows an integrated circuit 200 according to an embodiment of theinvention. As in FIG. 1, wafer 200 includes a substrate 110, BOX layer120, semiconductor layer 130, and a plurality of diodes 140A-140D withinsemiconductor layer 130. While shown herein as diodes, it should beunderstood that embodiments of the invention may employ one or moreother devices, including but not limited to a field effect transistor(FET), a thyristor, and a bipolar transistor. Wafer 200 also includes acontact 150A disposed adjacent diode 140A and extending fromsemiconductor layer 130, through BOX layer 120, and contacting ann-doped band 152A within substrate 110. Again, for the sake of clarity,only the n-doped bands and contacts of diodes 140B-140D necessary forillustration of the depicted embodiment of the invention are labeled inFIG. 2.

Substrate 110 and/or semiconductor layer 130 may include silicon(p-doped, n-doped, and/or undoped), high-resistivity silicon, germanium,silicon germanium, silicon carbide, and those consisting essentially ofone or more III-V compound semiconductors having a composition definedby the formula Al_(X1)Ga_(X2)In_(X3)As_(Y1)P_(Y2)N_(Y3)Sb_(Y4), whereX1, X2, X3, Y1, Y2, Y3, and Y4 represent relative proportions, eachgreater than or equal to zero and X1+X2+X3+Y1+Y2+Y3+Y4=1 (1 being thetotal relative mole quantity). Other suitable substrates include II-VIcompound semiconductors having a compositionZn_(A1)Cd_(A2)Se_(B1)Te_(B2), where A1, A2, B1, and B2 are relativeproportions each greater than or equal to zero and A1+A2+B1+B2=1 (1being a total mole quantity). In some embodiments, the substrate 10 mayinclude amorphous or polycrystalline silicon.

BOX layer 120 may include, for example, oxide, silicon oxide, silicondioxide, silicon oxynitride, silicon nitride (Si₃N₄), tantalum oxides,alumina, hafnium oxide (HfO₂), hafnium silicate (HfSi), plasma-enhancedchemical vapor deposition oxide, tetraethylorthosilicate (TEOS),nitrogen oxides, nitrided oxides, aluminum oxides, zirconium oxide(ZrO₂), zirconium silicate (ZrSiO_(x)), high K (K>5) materials, and/orcombinations thereof.

Contact 150A may include any conductive material, including, but notlimited to, polysilicon, tungsten, silicon, and/or combinations thereof.Other useful materials include, for example, aluminum, analuminum-copper alloy, cobalt, cobalt silicide, copper, metal silicide,nickel, nickel silicide, a nitrided metal, palladium, platinum, arefractory metal, such as ruthenium, tantalum nitride, titanium,titanium aluminum nitride, titanium nitride, titanium silicide, atitanium-tungsten alloy, and/or combinations thereof.

Dopants useful in forming, for example, n-doped band 152A include, butare not limited to, phosphorus, arsenic, antimony, sulphur, selenium,tin, silicon, and carbon. P-type dopants include, for example, but arenot limited to: boron, indium, and gallium.

N-doped band 152A shields diode 140A, such that a difference in voltagepotential 141A between diode 140A and substrate 110 is minimized. Thus,as can be seen in FIG. 2, difference in voltage potential 141A issubstantially the same as the differences in voltage potentials 141B,141C, and 141D between substrate 110 and diodes 140B, 140C, and 140D,respectively. That is, in wafer 200, differences in voltage potential donot increase along series-connected diodes as one approaches theterminal diode as they do in wafer 100 of FIG. 1. As such, embodimentsof the invention permit the use of higher voltage devices and/or alarger number of devices connected in series, and therefore a highertotal voltage, without degrading the breakdown voltage of theseries-connected device or the loss of voltage through leakage.

The voltages of individual devices (e.g., diodes 140A-D) as well as thetotal voltage of the series-connected devices will depend, for example,on their application and the number of devices so connected. In someembodiments, voltages of individual devices are between about 10 V andabout 50 V and total voltages are between about 20 V and about 150 V.Such voltages are exemplary, however, and are not limiting of the scopeof the various embodiments of the invention.

In some embodiments of the invention, an end 153A of n-doped band 152Aextends laterally beyond an end 143A of diode 140A, providing an overlapportion 154A. Such an arrangement helps control an electric fieldinduced by diode 140 and ensures that substrate 110 does not act to gatediode 140A.

Similarly, in some embodiments of the invention, a space 156A remainsbetween adjacent n-doped bands 152A, 152B. That is, a second end 155A ofn-doped band 152A is separated within substrate 110 from a first end153B of n-doped band 152B. Space 156A is large enough to ensure thatn-doped band 152A and n-doped band 152B do not act as a single shield,which would cause the depletion regions of each diode 140A, 140B tointersect, resulting in a single voltage potential for the two diodes140A, 140B.

FIG. 3 shows an integrated circuit 300 according to another embodimentof the invention. Here, a plurality of deep diodes 240A-240D areconnected in series within a thick semiconductor layer 230. Each deepdiode (e.g., 240A) includes stacked p-doped regions 242A, 246A andstacked n-doped regions 244A, 248A, such that a shallow trench isolation260A and deep trench isolation 262A are formed in semiconductor layer230 adjacent each deep diode. Thick semiconductor layer 230 permits theincorporation of an internal isolation 247A within deep diode 240A. Thatis, internal isolation 247A isolates p-doped region 246A from n-dopedregion 248A but does not extend through to BOX layer 220.

FIG. 4 shows an integrated circuit 400 according to another embodimentof the invention, in which a p-doped band 352A is used in an n-typesubstrate. The shielding properties of wafer 400 are similar, therefore,to those of wafer 200 in FIG. 2.

FIG. 5 shows an integrated circuit 500 according to yet anotherembodiment of the invention. In wafer 500, a plurality of high-voltagen-type field effect transistors (n-FETs) are connected in series. (Forthe sake of clarity, FIG. 5 shows only two n-FETs 440A, 440B, althoughany number of such devices may be connected in series, and only thefeatures of n-FET 440A are labeled.) Each n-FET 440A, 440B includes apolysilicon gate 480A, polysilicon conductors 446A, 448A, a p-well 470A,n-wells 442A, 444A, and a gate oxide formed from shallow trenchisolation (STI) 460A. In wafer 500, n-doped band 452A shields n-FET 440Asimilarly to the shielding of diode 140A in FIG. 2.

FIG. 6 shows an integrated circuit 600 according to still anotherembodiment of the invention. Wafer 600 is similar to wafer 200 of FIG.2, but each n-doped band 652A, 652B, 652C, 652D is biased to a voltageV₁, V₂, V₃, V₄, respectively. Each voltage V₁, V₂, V₃, V₄ is optimizedto reduce voltage leakage or increase breakdown voltage (V_(br)) of itsrespective diode 640A, 640B, 640C, 640D.

The foregoing description of various aspects of the invention has beenpresented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed, and obviously, many modifications and variations arepossible. Such modifications and variations that may be apparent to aperson skilled in the art are intended to be included within the scopeof the invention as defined by the accompanying claims.

1. An integrated circuit comprising: a semiconductor-on-insulator (SOI)wafer including: a p-type substrate; a buried oxide (BOX) layer atop thep-type substrate; and a semiconductor layer atop the BOX layer; aplurality of high voltage (HV) devices connected in series within thesemiconductor layer; an n-doped band within the p-type substrate andbelow a first of the plurality of HV devices; an additional n-doped bandwithin the p-type substrate and below a second of the plurality of HVdevices; a contact extending from the semiconductor layer and throughthe BOX layer to the n-doped band; and an additional contact extendingthrough the BOX layer to the additional n-doped band between andconnected in series to the second and a third of the plurality of HVdevices.
 2. The integrated circuit of claim 1, wherein each of theplurality of HV devices is independently selected from a groupconsisting of: a diode, a field effect transistor (FET), a thyristor,and a bipolar transistor.
 3. The integrated circuit of claim 1, whereinthe contact includes at least one conductive material selected from agroup consisting of: polysilicon, tungsten, and silicon.
 4. Theintegrated circuit of claim 1, wherein a difference in voltage potentialbetween the substrate and at least one of the plurality of HV devices isbetween about 20 V and about 150 V.
 5. The integrated circuit of claim1, wherein the n-doped band includes at least one dopant selected from agroup consisting of: phosphorus, arsenic, and antimony.
 6. Theintegrated circuit of claim 1, wherein the n-doped band and theadditional n-doped band are separated within the substrate by a spacefilled with a material of the p-type substrate.
 7. The integratedcircuit of claim 1, wherein the contact is connected in series betweenthe first and a second of the plurality of HV devices.
 8. The integratedcircuit of claim 1, wherein a portion of the doped band extendslaterally beyond an end of the first of the plurality of HV devices. 9.The integrated circuit of claim 1, wherein the substrate is selectedfrom a group consisting of: p-doped silicon, high-resistivity silicon,and n-doped silicon.
 10. The integrated circuit of claim 1, wherein thesemiconductor layer includes at least one material selected from a groupconsisting of: p-doped silicon, high-resistivity silicon, and n-dopedsilicon.
 11. The integrated circuit of claim 1, wherein the doped bandis biased to a voltage.
 12. The integrated circuit of claim 1, whereinthe doped band is connected in series to the first of the plurality ofHV devices and a second of the plurality of HV devices.
 13. Theintegrated circuit of claim 1, wherein at least one of the plurality ofHV devices includes an internal isolation that does not reach the BOXlayer.
 14. An integrated circuit comprising: asemiconductor-on-insulator (SOI) wafer including: a substrate; a buriedoxide (BOX) layer atop the substrate; and a semiconductor layer atop theBOX layer; at least one high voltage (HV) device within thesemiconductor layer; an n-doped band within the substrate and below theat least one HV device; and a contact extending from the semiconductorlayer and through the BOX layer to the n-doped band, wherein a portionof the n-doped band extends laterally beyond an end of the at least oneHV device.
 15. The integrated circuit of claim 14, wherein the at leastone HV device includes a plurality of HV devices and each of theplurality of HV devices is independently selected from a groupconsisting of: a diode, a field effect transistor (FET), a thyristor,and a bipolar transistor.
 16. The integrated circuit of claim 14,wherein the contact includes at least one conductive material selectedfrom a group consisting of: polysilicon, tungsten, silicon, aluminum, analuminum-copper alloy, cobalt, cobalt silicide, copper, metal silicide,nickel, nickel silicide, a nitrided metal, palladium, platinum, arefractory metal such as ruthenium, tantalum nitride, titanium, titaniumaluminum nitride, titanium nitride, titanium silicide, atitanium-tungsten alloy, and combinations thereof.
 17. The integratedcircuit of claim 14, wherein the n-doped band is operable to be biasedto a voltage.
 18. An integrated circuit comprising: asemiconductor-on-insulator (SOI) wafer including: a p-type substrate; aburied oxide (BOX) layer atop the substrate; and a semiconductor layeratop the BOX layer; a first high voltage (HV) device and a second HVdevice connected in series within the semiconductor layer; a firstn-doped band within the substrate and below the first HV device; asecond n-doped band within the substrate and below the second HV device;a first contact extending from the semiconductor layer and through theBOX layer to the first n-doped band; and a second contact extending fromthe semiconductor layer and through the BOX layer to the second n-dopedband, wherein the first n-doped band and the second n-doped band areseparated within the p-type substrate by a space, a portion of the firstn-doped band extends laterally beyond an end of the first HV device, anda portion of the second n-doped band extends laterally beyond an end ofthe second HV device.
 19. The integrated circuit of claim 18, whereineach of the first HV device and the second HV device is independentlyselected from a group consisting of: a diode, a field effect transistor(FET), a thyristor, and a bipolar transistor.
 20. The integrated circuitof claim 18, wherein: the p-type substrate includes at least one dopantselected from a group consisting of: boron, indium, and gallium; then-doped band includes at least one dopant selected from a groupconsisting of: phosphorus, arsenic, antimony, sulphur, selenium, tin,silicon, and carbon; each of the first contact and the second contact isindependently selected from a group consisting of: polysilicon,tungsten, silicon, aluminum, an aluminum-copper alloy, cobalt, cobaltsilicide, copper, metal silicide, nickel, nickel silicide, a nitridedmetal, palladium, platinum, a refractory metal such as ruthenium,tantalum nitride, titanium, titanium aluminum nitride, titanium nitride,titanium silicide, a titanium-tungsten alloy, and combinations thereof;and the BOX layer includes at least one material selected from a groupconsisting of: oxide, silicon oxide, silicon dioxide, siliconoxynitride, silicon nitride (Si₃N₄), tantalum oxides, alumina, hafniumoxide (HfO₂), hafnium silicate (HfSi), plasma-enhanced chemical vapordeposition oxide, tetraethylorthosilicate (TEOS), nitrogen oxides,nitrided oxides, aluminum oxides, zirconium oxide (ZrO₂), zirconiumsilicate (ZrSiO_(x)), high K (K>5) materials, and combinations thereof.21. An integrated circuit comprising: a semiconductor-on-insulator (SOI)wafer including: a substrate; a buried oxide (BOX) layer atop thesubstrate; and a semiconductor layer atop the BOX layer; a plurality ofhigh voltage (HV) devices connected in series within the semiconductorlayer; a doped band within the substrate and below a first of theplurality of HV devices; and a contact extending from the semiconductorlayer and through the BOX layer to the doped band, wherein the contactis connected in series between the first and a second of the pluralityof HV devices.
 22. An integrated circuit comprising: asemiconductor-on-insulator (SOI) wafer including: a substrate; a buriedoxide (BOX) layer atop the substrate; and a semiconductor layer atop theBOX layer; a plurality of high voltage (HV) devices connected in serieswithin the semiconductor layer; a doped band within the substrate andbelow a first of the plurality of HV devices; and a contact extendingfrom the semiconductor layer and through the BOX layer to the dopedband, wherein a portion of the doped band extends laterally beyond anend of the first of the plurality of HV devices.
 23. An integratedcircuit comprising: a semiconductor-on-insulator (SOI) wafer including:a substrate; a buried oxide (BOX) layer atop the substrate; and asemiconductor layer atop the BOX layer; a plurality of high voltage (HV)devices connected in series within the semiconductor layer; a doped bandwithin the substrate and below a first of the plurality of HV devices;and a contact extending from the semiconductor layer and through the BOXlayer to the doped band, wherein the doped band is connected in seriesto the first of the plurality of HV devices and a second of theplurality of HV devices.
 24. An integrated circuit comprising: asemiconductor-on-insulator (SOI) wafer including: a substrate; a buriedoxide (BOX) layer atop the substrate; and a semiconductor layer atop theBOX layer; a plurality of high voltage (HV) devices connected in serieswithin the semiconductor layer; a doped band within the substrate andbelow a first of the plurality of HV devices; and a contact extendingfrom the semiconductor layer and through the BOX layer to the dopedband, wherein at least one of the plurality of HV devices includes aninternal isolation that does not reach the BOX layer.